Office chairs have, above a height-adjustable support part which in this application is regarded as belonging to the chassis, a seat surface and a backrest, which are jointly rotatable about a common vertical axis, in most cases the vertical axis of the support part, and are pivotable about at least a horizontal axis individually or dependently on each other. Mechanisms are available by which the pivoting movement takes place about an axis that is not fixed in position relative to the support part, but in which the position of the axis changes (but in most cases one to one) during the pivoting.
A problem in all such chair kinematics is, on the one hand, the relatively small available space and, on the other hand, the not inconsiderable forces and moments that occur, and the desire, sometimes even a necessity, to switch off the pivotability about individual axes, which in the jargon is called fixing an axis.
What is needed is a kinematic mechanism that meets these conditions in a simple, cost-effective and mechanically stable way.